1. Field of the Invention
The present invention relates to a plasma processing apparatus and method of the capacitive coupling type, used for performing a plasma process on a target substrate in, e.g., a semiconductor processing system. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, plasma etching processes are often used to form circuits on a semiconductor wafer treated as a target substrate. There are various plasma etching apparatuses for performing such plasma etching, but parallel-plate plasma processing apparatuses of the capacitive coupling type are presently in the mainstream.
In general, a parallel-plate plasma etching apparatus of the capacitive coupling type includes a chamber with parallel-plate electrodes (upper and lower electrodes) disposed therein. While a process gas is supplied into the chamber, an RF (radio frequency) is applied to one of the electrodes to form an RF electric field between the electrodes. The process gas is ionized into plasma by the RF electric field, thereby performing a plasma etching process on a semiconductor wafer.
In recent years, design rules for ULSIs have been increasingly miniaturized, and the shape of holes is required to have a higher aspect ratio. For this reason, there is a proposal to use an application RF power with a higher frequency, so as to generate high density plasma while maintaining a good dissociation state of the plasma. This method makes it possible to suitably generate plasma under a lower pressure, which can meet miniaturization of design rules.
However, even where such an RF power with a higher frequency is used, plasma uniformity is still unsatisfactory. In order to solve this problem, Jpn. Pat. Appln. KOKAI Publication No. 2000-323460 (Patent Document 1) discloses a plasma processing technique. According to this technique, an upper electrode is supplied with a DC (direct current) voltage, as well as an RF power with a frequency of 27 MHz or more, to control plasma so as to uniformize the plasma density.
Where a DC voltage is applied as in the technique disclosed in Patent Document 1, the application timing of the DC voltage should be influential on plasma generation. However, Patent Document 1 is silent about the application timing of the DC voltage to generate stable and good plasma.